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[aprssig] Digipeater solutions (rambling)

Wes Johnston aprs at kd4rdb.com
Tue Nov 2 23:09:07 UTC 2004


I think it was Tate who said that out west some truckers _need_ 5 hops just to
get to an IGATE....

At first I was in favor of asking Steve Dimse to add "BAD PATH" and a bunch of
carriage returns to make the maps.... errr difficult... to see.  This would
cause the spouses of the offending stations to get in touch with them and would
be more effective than _me_ trying to get to them.  But, alas, Tate made a good
point and got me thinking...

The real problem here is that _my_ digipeater is basically stupid.  Short of
Kantronics giving us the ability to cap the number of hops, or giving us
pre-emptive digipeating so we could do things like substitute a path of WIDE7-7
down to the local custom (like digined does), we aren't going to go anywhere
fast.  Does anyone know what they charge per hour?  I wonder if the cost of a
firmware mod for the kpc3plus were in the range of 500 to 800 (I really have NO
idea how many hours this would take, heck I still don't know EXACTLY what I'd
like them to do), if any of us would be willing to pool enough money to pay
them for the project?  I certainly do NOT expect them to make a firmware change
for free.  Of course this still leaves us with the problem of the unsupported
kpc3 units out there.

The idealistic part of me is starting to think that a trucker should be able to
run a path like RELAY, WIDE7-7,IGATE , and our local digipeater should see
IGATE in there and rewrite his whole path to get his packet to an igate.  Or
substitute WIDEx-y in place of WIDE7-7....

Of course the practical side of me says this isn't going to happen any time
soon.  BUT ideally, the network should take the _intended_ target (whether it
be an IGATE or the ALOHA range) and massage the path to make it happen while
still allowing people to specify very specific "untouchable" paths which no
digipeaters would try to fix...

Wouldn't it be neat to send a packet with the path RELAY,ALOHA and have it go
out just far enough to cover the local aloha range?

Or RELAY,WIDE2-2,IGATE and have it routed to the nearest IGATE?

Short of someone writing a new EPROM for the KPC3, or creating some sort of a
clip on daughter board, I think the easiest is going to be a kiss mode
digipeater module that plugs into the serial port.

I think this digipeater would need to be remotely configurable, but without
writing all the connected mode ax.25 stuff.... one way to do this would be to
generate a 16 bit checksum that was XOR'ed and initialized with a seed that
only the digi owner would know.  You could send a command to the digi as an
APRS message with the checksum at the end.  Others would see the checksum, but
without knowing the seed, they wouldn't be able to generate any NEW commands. 
I'm sure that Scott will tell us about TEA and other encryption methods easy
for an 8 bit microprocessor... the important thing here is that we'd be able to
securely control the digipeater with an APRS message.

Just me thinking...
Wes




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